Experimental distinction of damping mechanisms during hydraulic transients in pipe flow

The aim of the present paper is to contribute to the identification of the principal mechanical-hydraulical relationships during hydraulic transients by means of the analysis of observed transient pressure and strain waves in different pipe rigs. Four different experimental set-ups are analysed: a straight copper pipe with either moving or anchored downstream pipe-end, a coil copper pipe and a coil polyethylene pipe. Discussion highlights differences in the response of each system in terms of wave shape, damping, and dispersion. The straight copper pipe behaviour, for an anchored pipe-end, has shown the closest dynamic response to the expected one from classical waterhammer theory, being unsteady friction the most relevant damping mechanism. Fluid structure interaction dominates when the valve is released in the straight copper pipe and also has an important role in the coil copper pipe. Viscoelasticity dominates in the polyethylene pipe.